2 5 2 5 1.0 :; 1111128 1//// . :; 111112 8 11111 . Ww I~ 2.2 : I~ I 2.2 ~ W '"'w Ii£ w ~ ~ ~ ~ ~ 1.1 1.1 ...,a~ ... -- 111111.8 111111.8 '111111. 25 IIIII~ 111111.6 111111.25 111111.4 111111.6 MICROCOPY RESOLUTION TEST CH>XRT (MICROCOPY RESOLUTION TEST CHART NATIONAL BURlAU or SlANO;'RD~·196 H NATiONAL BUREAU OF SlA.NDARDS-1963·A ==========~=~:~========~TECHNICAL BULU'.TIN No. Z8~FEBRUARY. 19Z8 UNITlm:STATES DEPARTMENT OF AGRICULTURE WASHINGTON, D. C. CLOVER ANTHRACNOSE CAUSED BY COLLETOTRICHUM TRIFOLII By JOHN MONTEITH, Jr. ABsociate Pathologist, Office of Vegetable and Forage Diseases, Bureau of Plant Industry 1 CONTENTS Page Page rntroductlon _____________________ 1 The funguR in relntlon to anthrac­ ElIstol'Y and geogro9hlcal dlstrlbu- ., nos~('ontlnul'd. tlon___________________________ 3- Vlabillty Bnd longe't'lty ot DlY~ flost plnnts______________________ lIum and conidia ___________ 13 SYlI1ptom~ _______________________ 3 Dlsspmluution of conidla_______ 13 Inj lIty produced __________________ II Method of Infection and period The cau~,,1 ol'J~nnlsm--------------, 7 of Incubntlon_______________ 13 Tllxonomy __________.:.________ 7 Source of natural Infl'ctlon____ 14 l~olll t1ous____________________ 8 Environmental factors Influencing oc­ Spore germlnntlon ____________ 8 currence and progress of the dla- Cull ural characters ___________ 9 ease__________________________ 15 Helu tlon of tpllIpero ture to '.:'em peruture _________________ 15 growth 011 medIa ___________ \l hlolsture ____________________ 17 Errect of I\ght________________ 11 Cor.trol__________________________ 19 Elfpct of nchllty______________ 11 I'nthol,enlclty ________________ 11 Anthracnose-resistant clover____ 20 Eorelgngrown comparedseed ________________ with home­ 21 ThenORe fungus ____ .._____________________In relutlon to anthrac­ 12 Til;!clover development_____________________ of resIstant 21 Sensonnl devplopm~lIt of host and para~lte _______________ 12 Summary_~______________________ 23 Spore production _____________ 12 Literature cited __________________ 25 INTRODUCTION The inability of red clover to maintain its relative position of prominence in the American farming system has been generally at­ tributed to the frequent recurrence of what has been indefinitely termed "clover failure." It is well recognized that several factors sepa­ rately or collectively may cause failure of a clover crop (17).2 Dis­ eases unquestionably contribute largely to these losses, and under certain conditions they are the sole agents responsible for destruction of the crop. In the United States the most important disease of clover thus far reported is anthracnose. There are, however, several 1 This studl was begun at the suggestion of A. d. Pieters, of the Olllce of Forage CroPII, and mucb 0 It, eSllecially the field phases, wns done In cooperation with him. The author wIshes to express his appreclotlon of Doctor Pleters's Interest and aid throughout the progr~ss ot the work, 1'he grt'l!nhouse and laboratory studies were conducted In coo\1f'rnlion with the department of plant pathology, Unh'prslty of Wisconsin. a Reference Is made by number (italic) to .. Literature cited," p. 25. 119332-28--1 2 TEOHNICAL BULLETIN 28, U. S. DEPT. OF AGRICULTURE fungi described as causing clover anthracnose, chief of which are OolletotriclLum trifolii Bain and Essary (5) and Gloeosporium cGlUliv01'Um Kirchner (11 ) . The scattered literature on this subject and reports received by the Plant Disease Survey of the Bureau of Plant Industry, indicate that these two fungi are frequently confused or at times regarded as identical (8, 10, 933). .An investigation undertaken for the purpose of defining somewhat more clearly the role played by plant disease in clover failure led at once to a study of the relationship between these two important anthracnose-producing fungi. The phases which appeared to be of primary importance were those dealing with the influence of environmental factors on the distribution and sever­ it;r of these diseases and the relative susceptibility of clovers of dIfferent origin to their attacks. It was soon evident that the two fungi, although producing very similar disease symptoms', were entirely distinct species-a distinction not foundeel merely on varia­ tions due to environment affecting spore characters or occurrence of setae. It is the purpose of this bulletin to summarize the present knowled~e of clover anthracnose produced by Oolletot1'ichu1rb t?ifolii. The silmlal' Jisease produced by (floeollporiwln caulivorurn is to be considered in a later paper. HISTORY AND GEOGRAPHICAL DISTRIBUTION In 1905 the botany department of the Tennessee Agricultural Experiment Station (4) undertook a survey of the State to determine the cause of repeated failures of red clover, which had threatened the success of this important crop throughout many of the best farming districts of Tennessee. In the course of the investigation saveral diseases were observed producing more or less injury to clover, but their combined damage was found to be of minor hupor­ tance when compared with the losses caused by a new fungus, 001­ letotrichwm trifolii, which was described by Bain and Essary in 1906 (5,6). At about the time it was discovered in Tennessee, .T. M. Westgate found the same disease causing serious damage on alfrMa in Virgmia and sent specimens to Mrs. F. W. Patterson of the Department of Agriculture. Mrs. Patterson later sent her notes and ;Illaterial to Professor Bain, who identified the causal organism of the alfalfa disease as identical with that found in Temlef:See on clover (5). In 1905 Sheldon (fJO) reported an undetermined anthracnose fungus found on red clover in West Virginia; the following year he identified O. &rifolii (931). In 190() (5) the disease was recorded as ocCUrril'lO' in Tennessee, Vir~inia, West Virginia, Kentucky, Arkansas, and Ohio. The fol­ 10'Nmg year it was found in Delaware (9) and soon afterwards was reported from neighboring States. At present there are records of its occurrence in practically every State in the eastern and mid­ weetern cl~ver belt, with the exceptlOn of the New England States, as well as m southern Canada. Except for a :case on alfalfa in South Africa (1), the disease has nllt been reported outside of 'North America. OLOVER ANTHRAONOSE 3 HOST PLANTS Oolletotrichum, t1ifolii is regarded as a l.lmgus which attacks prin­ cipally red clover (T7ifolium pratense). It is common, however, on alfalfa (Meilicago sativa) in nearly every section where it occurs on clover. It is also found on crimson clover (T. incarnatwm), subter­ ranean clover (T. subterran(Jum) l bur clover (Medicago Mspida) , and sweet clover (Itielilotus alba). Recent inoculations in the green­ house have shown tllat all of tllese are readily infected with this organism. No attempt has been made to cletermine the complete host range of the parasite, although the facility with which it attacks the above-named hosts in three different genera would indicate that it has a much wider range of hosts than is ordinarily assum'i!d. On the other hand, it is by no means an omnivorous parasite even within the Leguminosae. It has not been observed on white clover, and artificial greenhouse inoculations failed to produce the disease on beans (PAaseovus v1tlgmis) , peas (PiSU111, sativu111,) , Japan clover (LeS1JeCZeen st1iata) , Korean lespedeza (L. stipulacea) , or white lupine (Llbpinus albus). Alsike clovel' (T. hyb1idum) is practically immune (6). The inclusion of alfalfa und sweet clover as common hosts for OoUetotnch1t'>n trifolii is an important distinction between this fungus and Gloeosp01ium caulivorumj the latter has so far not been. reported on those plants except where based on Saccardo's (19, p. 1201) obvious error in listing Medicago sativa as the host rather than Trifolium pratense which was given in Kirchner's (11) original description. ' SYMPTOMS Oolletot1~ichu1n t1ifolii occurs on any green part of the plant and on the upper portion of the taproot. It may attack plants at any time in their development from the seedling stage to maturity. On the le:wes the disease occurs as dark-brown or blackened lesions of irregular shape and varying in size from a minute spot to a gen­ eral infection covering the entire leaf blade. As a rule these lesions are more common near the margin and are frequently more or less angular in shape, conforming to the venation of the leaf. As they commonly occur in the field, there is nothing macroscopically distinc­ tive in these lesions which will serve as a positive identification when found with some of the other leaf spots of clover. In the original description (5) it was stated that the disease was rarely found on the leaves, and the statement has since been repee.ted by several writers. This observation may have been due to confusing the Colletotrichum lesions with some other leaf spots. However, fields are frequently found in which there is a relatively large proportion of leaf infec· tion. Plate 1 shows the disease on leaves of red clover and sweet clover as produced by artificial inoculation with a pure culture of O. trifoUi. The lesions occurring on sweet-clover leaves are much more sharply defined than in the case of red clover and are a lig'h~er brown in the center, with a distinct reddish brown or black border, especially in the younO'er dark-green leaves such as are shown on the right in Plate 1, A. This greater color differentiation, as compared WIth red clover, applies also to a somewhat less extent to the suscepti­ ble species of Medicago. 4 TECHNIOAL BULLETIN 28, U. S. DEPT. OF AGRIOULTURE One of the most frequent points of attack is the short stalk of the leaflet. There the lesion may be limited to a single stalk, or it may extend out through the leaf blade or back to the pehole, from where it is likely to pass to the other leaflets. As a result of such infection the leafstalks become black and shriveled, causing the leaflet to \'~roop.